1. Field of the Invention
This invention relates in general to bridging hanger support within a wellhead assembly, and more particularly to a structure to increase bridging hanger seal capacities.
2. Brief Description of Related Art
A subsea well assembly includes a wellhead housing that is secured to a large diameter conductor pipe extending to a first depth in the well. After drilling to a second depth through the conductor pipe, a string of casing is lowered into the well and suspended in the wellhead housing by a casing hanger. A packoff seals between an outer diameter portion of the casing hanger and the bore of the wellhead housing. Some wells have two or more strings of casing, each supported by a casing hanger in the wellhead housing.
In one type of completion, a string of production tubing is lowered into the last string of casing. A tubing hanger lands and seals to the upper casing hanger. The production tubing string is suspended from the tubing hanger and the well is then produced through the tubing. Prior to running the tubing and the tubing hanger, the operator will pressure test the upper casing hanger packoff. The packoff may be unable to pass the pressure test, possibly due to damage on the interior wall of the wellhead housing. If so, one remedy is to install an emergency or bridging hanger in the wellhead housing. The bridging hanger does not support a string of casing, but has an interior profile that is normally the same as the profile in the upper casing hanger. The operator lands and seals the lower portion of the bridging hanger to the casing hanger. The operator installs a packoff between the upper exterior portion of the bridging hanger and the wellhead housing above the casing hanger. The operator then runs the tubing and lands and seals the tubing hanger in the bridging hanger.
As wellbore depths have increased, pressures within the wellbore have increased, exerting increasingly higher loads against the hangers suspending casing and liner strings. In situations where bridging hangers are needed to supplement a casing hanger packoff, these pressures may be larger than the maximum pressure ratings of the bridging hangers. Consequently, after landing and setting the bridging hanger, the wellbore pressure may cause the packoff sealing the bridging hanger to the wellbore to fail, making the bridging hanger unsuitable for landing of a subsequent tubing hanger. Therefore, there is a need for an apparatus and method to increase the pressure ratings of the bridging hanger and its corresponding seals.